aut Scylla latrans infima inguinum parteor Scylla barking from the lowest part of her loins

tam mente dura procreavit ac taetradid not give birth to you with such a rough and cruel mind.
"did not" from "num"

ut supplicis vocem in novissimo casuso that you have would have a disregarding voice in the greatest misfortune of the supplicant,

contemptam haberes, a nimis fero corde?Alas! (you) with an excessively cruel heart?
~Book says fero corde is dependent on the implied vocative but I think it makes sense without.
"So that you, in the greatest misfortune of the supplicant, would have a disregarding voice with, alas, an excessively cruel heart"